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author | Simon Peyton Jones <simonpj@microsoft.com> | 2021-02-11 14:44:20 +0000 |
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committer | Ben Gamari <ben@smart-cactus.org> | 2021-02-19 11:03:46 -0500 |
commit | 4196969c53c55191e644d9eb258c14c2bc8467da (patch) | |
tree | bb4608ff96e916c204b6837405690190b70c59db /compiler/GHC/Tc/Gen/Expr.hs-boot | |
parent | f78f001c91736e31cdfb23959647226f9bd9fe6b (diff) | |
download | haskell-4196969c53c55191e644d9eb258c14c2bc8467da.tar.gz |
Improve handling of overloaded labels, literals, lists etcwip/T19154
When implementing Quick Look I'd failed to remember that overloaded
labels, like #foo, should be treated as a "head", so that they can be
instantiated with Visible Type Application. This caused #19154.
A very similar ticket covers overloaded literals: #19167.
This patch fixes both problems, but (annoyingly, albeit temporarily)
in two different ways.
Overloaded labels
I dealt with overloaded labels by buying fully into the
Rebindable Syntax approach described in GHC.Hs.Expr
Note [Rebindable syntax and HsExpansion].
There is a good overview in GHC.Rename.Expr
Note [Handling overloaded and rebindable constructs].
That module contains much of the payload for this patch.
Specifically:
* Overloaded labels are expanded in the renamer, fixing #19154.
See Note [Overloaded labels] in GHC.Rename.Expr.
* Left and right sections used to have special code paths in the
typechecker and desugarer. Now we just expand them in the
renamer. This is harder than it sounds. See GHC.Rename.Expr
Note [Left and right sections].
* Infix operator applications are expanded in the typechecker,
specifically in GHC.Tc.Gen.App.splitHsApps. See
Note [Desugar OpApp in the typechecker] in that module
* ExplicitLists are expanded in the renamer, when (and only when)
OverloadedLists is on.
* HsIf is expanded in the renamer when (and only when) RebindableSyntax
is on. Reason: the coverage checker treats HsIf specially. Maybe
we could instead expand it unconditionally, and fix up the coverage
checker, but I did not attempt that.
Overloaded literals
Overloaded literals, like numbers (3, 4.2) and strings with
OverloadedStrings, were not working correctly with explicit type
applications (see #19167). Ideally I'd also expand them in the
renamer, like the stuff above, but I drew back on that because they
can occur in HsPat as well, and I did not want to to do the HsExpanded
thing for patterns.
But they *can* now be the "head" of an application in the typechecker,
and hence something like ("foo" @T) works now. See
GHC.Tc.Gen.Head.tcInferOverLit. It's also done a bit more elegantly,
rather than by constructing a new HsExpr and re-invoking the
typechecker. There is some refactoring around tcShortCutLit.
Ultimately there is more to do here, following the Rebindable Syntax
story.
There are a lot of knock-on effects:
* HsOverLabel and ExplicitList no longer need funny (Maybe SyntaxExpr)
fields to support rebindable syntax -- good!
* HsOverLabel, OpApp, SectionL, SectionR all become impossible in the
output of the typecheker, GhcTc; so we set their extension fields to
Void. See GHC.Hs.Expr Note [Constructor cannot occur]
* Template Haskell quotes for HsExpanded is a bit tricky. See
Note [Quotation and rebindable syntax] in GHC.HsToCore.Quote.
* In GHC.HsToCore.Match.viewLExprEq, which groups equal HsExprs for the
purpose of pattern-match overlap checking, I found that dictionary
evidence for the same type could have two different names. Easily
fixed by comparing types not names.
* I did quite a bit of annoying fiddling around in GHC.Tc.Gen.Head and
GHC.Tc.Gen.App to get error message locations and contexts right,
esp in splitHsApps, and the HsExprArg type. Tiresome and not very
illuminating. But at least the tricky, higher order, Rebuilder
function is gone.
* Some refactoring in GHC.Tc.Utils.Monad around contexts and locations
for rebindable syntax.
* Incidentally fixes #19346, because we now print renamed, rather than
typechecked, syntax in error mesages about applications.
The commit removes the vestigial module GHC.Builtin.RebindableNames,
and thus triggers a 2.4% metric decrease for test MultiLayerModules
(#19293).
Metric Decrease:
MultiLayerModules
T12545
Diffstat (limited to 'compiler/GHC/Tc/Gen/Expr.hs-boot')
-rw-r--r-- | compiler/GHC/Tc/Gen/Expr.hs-boot | 6 |
1 files changed, 4 insertions, 2 deletions
diff --git a/compiler/GHC/Tc/Gen/Expr.hs-boot b/compiler/GHC/Tc/Gen/Expr.hs-boot index b47b146118..22abe79491 100644 --- a/compiler/GHC/Tc/Gen/Expr.hs-boot +++ b/compiler/GHC/Tc/Gen/Expr.hs-boot @@ -1,7 +1,8 @@ module GHC.Tc.Gen.Expr where import GHC.Hs ( HsExpr, LHsExpr, SyntaxExprRn , SyntaxExprTc ) -import GHC.Tc.Utils.TcType ( TcRhoType, TcSigmaType, SyntaxOpType, ExpType, ExpRhoType ) +import GHC.Tc.Utils.TcType ( TcRhoType, TcSigmaType, SyntaxOpType + , ExpType, ExpRhoType, ExpSigmaType ) import GHC.Tc.Types ( TcM ) import GHC.Tc.Types.Origin ( CtOrigin ) import GHC.Core.Type ( Mult ) @@ -21,7 +22,8 @@ tcCheckMonoExpr, tcCheckMonoExprNC :: -> TcRhoType -> TcM (LHsExpr GhcTc) -tcExpr :: HsExpr GhcRn -> ExpRhoType -> TcM (HsExpr GhcTc) +tcPolyExpr :: HsExpr GhcRn -> ExpSigmaType -> TcM (HsExpr GhcTc) +tcExpr :: HsExpr GhcRn -> ExpRhoType -> TcM (HsExpr GhcTc) tcInferRho, tcInferRhoNC :: LHsExpr GhcRn -> TcM (LHsExpr GhcTc, TcRhoType) |